Physics stage 2: colliders gain the shapes capsule and polygon, a polygon keeps its corners in the property points, turns, scales and mirrors with its object and is edited in the scene view (drag a corner, click an edge to insert one, double-click to delete, at least three stay, each step one undo step), a concave polygon is split into convex parts, a self-intersecting one is drawn red and collides with nothing, Rapier gets a capsule and one convex collider per part on the same body, and Move and the editor run use our own f64 geometry for the new shapes, where on a tie between two normals the one that blocks the move least wins, so a box no longer stops at the foot of a slope (#151); first version of a collision outline per texture frame, edited in the texture tab with the new Collision toggle, which a plain tile blocks with instead of its rectangle (#141, to be reworked)

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/runtime/physics/PhysicsSystem.ts

@@ -8,8 +8,9 @@ import type {
 import { isHandleEnabled, worldMatrixOf } from '../../core/graph';
 import { apply, determinant, IDENTITY, invert, type Mat } from '../../core/model/matrix';
 import type { Vec2 } from '../../core/model/Properties';
+import { signedArea } from '../../core/model/polygon';
 import { parentChain } from '../../core/model/walk';
-import { type ColliderShape, isTrigger, shapesOverlap } from '../../core/properties/collider';
+import { type ColliderShape, isTrigger, shapeArea, shapesOverlap } from '../../core/properties/collider';
 import { hasTransformProps } from '../../core/properties/PropertySchema';
 import {
   type BodyType,
@@ -55,7 +56,9 @@ interface Pose {
 interface Body {
   kind: 'rigid' | 'free' | 'tilemap';
   body: RigidBody;
+  /** The engine's colliders – several for a polygon, one per convex piece – and whose each is. */
   colliders: Collider[];
+  sources: Entity[];
   /** What the colliders were built from; they are built again when it changes (a scaled object). */
   shapeKey: string;
   settingsKey: string;
@@ -277,7 +280,7 @@ export class PhysicsSystem implements System, CollisionSource {
     const mass = rigidbody ? rigidbodySettings(rigidbody.props).mass : 0;
     if (mass > 0) return mass;
     return blockingCollidersOf(world, entity).reduce(
-      (sum, c) => sum + colliderMaterial(c.props).density * areaOf(shapeOf(c)) * toMetres(1) ** 2,
+      (sum, c) => sum + colliderMaterial(c.props).density * shapeArea(shapeOf(c)) * toMetres(1) ** 2,
       0,
     );
   }
@@ -351,6 +354,7 @@ export class PhysicsSystem implements System, CollisionSource {
       kind: want.kind,
       body: this.engine!.createRigidBody(desc),
       colliders: [],
+      sources: [],
       shapeKey: '',
       settingsKey: '',
       turns: false,
@@ -372,7 +376,7 @@ export class PhysicsSystem implements System, CollisionSource {
     if (want.kind === 'tilemap') return { x: 0, y: 0, angle: 0 };
     if (want.kind === 'free') {
       const shape = shapeOf(key);
-      return { x: shape.x, y: shape.y, angle: shape.kind === 'box' ? shape.angle : 0 };
+      return { x: shape.x, y: shape.y, angle: shape.kind === 'circle' ? 0 : shape.angle };
     }
     return matrixPose(worldMatrixOf(key));
   }
@@ -433,15 +437,12 @@ export class PhysicsSystem implements System, CollisionSource {
   private build(body: Body, want: Wanted, key: Entity, world: World): void {
     const shapes = this.shapesWanted(want, key, world);
     const origin = body.placed;
-    const local = shapes.map(({ entity, shape }) => ({ entity, shape, at: relativeTo(origin, shape) }));
+    const local = shapes.map(({ entity, shape }) => ({ entity, shape, pieces: piecesInBody(origin, shape) }));
     const shapeKey =
       JSON.stringify(
-        local.map(({ entity, shape, at }) => [
+        local.map(({ entity, pieces }) => [
           entity.id,
-          shape.kind === 'box' ? [round(shape.w), round(shape.h)] : round(shape.r),
-          round(at.x),
-          round(at.y),
-          round(at.angle),
+          pieces.map(pieceKey),
           entity.type === 'collider' ? [isTrigger(entity.props), colliderMaterial(entity.props)] : 0,
         ]),
       ) + JSON.stringify(want.settings?.mass ?? 0);
@@ -452,26 +453,28 @@ export class PhysicsSystem implements System, CollisionSource {
         this.engine!.removeCollider(collider, true);
       }
       body.colliders = [];
+      body.sources = [];
       const mass = want.settings?.mass ?? 0;
-      const area = local.reduce((sum, { entity, shape }) => sum + (isSolid(entity) ? areaOf(shape) : 0), 0);
-      for (const { entity, shape, at } of local) {
-        if (areaOf(shape) <= 0) continue;
-        const desc = this.colliderDesc(
-          entity,
-          shape,
-          at,
-          mass > 0 && area > 0 ? (mass * areaOf(shape)) / area : 0,
-        );
-        const collider = this.engine!.createCollider(desc, body.body);
-        body.colliders.push(collider);
-        this.parts.set(collider.handle, { entity, shape, owner: body });
-      }
+      const area = local.reduce(
+        (sum, { entity, shape }) => sum + (isSolid(entity) ? shapeArea(shape) : 0),
+        0,
+      );
+      for (const { entity, shape, pieces } of local)
+        for (const piece of pieces) {
+          const share = mass > 0 && area > 0 ? (mass * pieceArea(piece)) / area : 0;
+          const desc = this.colliderDesc(entity, piece, share);
+          if (!desc) continue;
+          const collider = this.engine!.createCollider(desc, body.body);
+          body.colliders.push(collider);
+          body.sources.push(entity);
+          this.parts.set(collider.handle, { entity, shape, owner: body });
+        }
     }
     // Shapes are refreshed every tick even when the colliders stay: the overlap test reads them.
-    const built = local.filter(({ shape }) => areaOf(shape) > 0);
+    const shapeOfEntity = new Map(local.map(({ entity, shape }) => [entity, shape]));
     body.colliders.forEach((collider, i) => {
-      const { entity, shape } = built[i]!;
-      this.parts.set(collider.handle, { entity, shape, owner: body });
+      const entity = body.sources[i]!;
+      this.parts.set(collider.handle, { entity, shape: shapeOfEntity.get(entity)!, owner: body });
       const on = isHandleEnabled(entity);
       if (collider.isEnabled() === on) return;
       collider.setEnabled(on);
@@ -480,7 +483,7 @@ export class PhysicsSystem implements System, CollisionSource {
     });
     if (body.kind !== 'rigid') return;
     // Without a collider the engine would weigh it nothing, and a thing of no weight never falls.
-    const weighed = built.some(({ entity }) => isSolid(entity) && isHandleEnabled(entity));
+    const weighed = body.sources.some((entity) => isSolid(entity) && isHandleEnabled(entity));
     const own = weighed ? 0 : want.settings?.mass || 1;
     if (own !== body.ownMass) {
       body.ownMass = own;
@@ -494,13 +497,30 @@ export class PhysicsSystem implements System, CollisionSource {
     return want.colliders.map((entity) => ({ entity, shape: shapeOf(entity) }));
   }
 
-  private colliderDesc(entity: Entity, shape: ColliderShape, at: Pose, mass: number): ColliderDesc {
+  /** The engine collider of one piece; null for a piece of no size, which the engine would refuse. */
+  private colliderDesc(entity: Entity, piece: Piece, mass: number): ColliderDesc | null {
     const R = this.rapier;
-    const desc =
-      shape.kind === 'circle'
-        ? R.ColliderDesc.ball(toMetres(shape.r))
-        : R.ColliderDesc.cuboid(toMetres(shape.w / 2), toMetres(shape.h / 2));
-    desc.setTranslation(toMetres(at.x), toMetres(at.y)).setRotation(at.angle);
+    if (pieceArea(piece) <= 0) return null;
+    let desc: ColliderDesc | null;
+    switch (piece.kind) {
+      case 'ball':
+        desc = R.ColliderDesc.ball(toMetres(piece.r));
+        break;
+      case 'cuboid':
+        desc = R.ColliderDesc.cuboid(toMetres(piece.hw), toMetres(piece.hh));
+        break;
+      case 'capsule':
+        desc = R.ColliderDesc.capsule(toMetres(piece.half), toMetres(piece.r));
+        break;
+      case 'convex':
+        desc = R.ColliderDesc.convexHull(
+          new Float32Array(piece.points.flatMap((p) => [toMetres(p.x), toMetres(p.y)])),
+        );
+        break;
+    }
+    if (!desc) return null;
+    if (piece.kind !== 'convex')
+      desc.setTranslation(toMetres(piece.x), toMetres(piece.y)).setRotation(piece.angle);
     // A tile has no material of its own; it gets what a new collider starts with.
     const material = colliderMaterial(entity.type === 'collider' ? entity.props : {});
     desc.setFriction(material.friction).setRestitution(material.bounciness);
@@ -639,21 +659,71 @@ function blend(a: Pose, b: Pose, t: number): Pose {
   };
 }
 
-/** A world shape as seen from a body at `origin`: offset and turn in the body's own frame. */
-function relativeTo(origin: Pose, shape: ColliderShape): Pose {
-  const dx = shape.x - origin.x;
-  const dy = shape.y - origin.y;
+/**
+ * One engine collider in the body's own frame (world units): a ball, a box or a capsule placed and
+ * turned there, or a convex piece given by its corners.
+ */
+type Piece =
+  | { kind: 'ball'; x: number; y: number; angle: number; r: number }
+  | { kind: 'cuboid'; x: number; y: number; angle: number; hw: number; hh: number }
+  | { kind: 'capsule'; x: number; y: number; angle: number; half: number; r: number }
+  | { kind: 'convex'; points: Vec2[] };
+
+/** A world shape as seen from a body at `origin`, as the engine colliders that make it up. */
+function piecesInBody(origin: Pose, shape: ColliderShape): Piece[] {
   const cos = Math.cos(origin.angle);
   const sin = Math.sin(origin.angle);
-  return {
-    x: dx * cos + dy * sin,
-    y: -dx * sin + dy * cos,
-    angle: (shape.kind === 'box' ? shape.angle : 0) - origin.angle,
+  const toBody = (p: Vec2): Vec2 => {
+    const dx = p.x - origin.x;
+    const dy = p.y - origin.y;
+    return { x: dx * cos + dy * sin, y: -dx * sin + dy * cos };
   };
+  switch (shape.kind) {
+    case 'circle':
+      return [{ kind: 'ball', ...toBody(shape), angle: 0, r: shape.r }];
+    case 'box':
+      return [
+        {
+          kind: 'cuboid',
+          ...toBody(shape),
+          angle: shape.angle - origin.angle,
+          hw: shape.w / 2,
+          hh: shape.h / 2,
+        },
+      ];
+    case 'capsule': {
+      const a = toBody(shape.a);
+      const b = toBody(shape.b);
+      const half = Math.hypot(b.x - a.x, b.y - a.y) / 2;
+      const mid = { x: (a.x + b.x) / 2, y: (a.y + b.y) / 2 };
+      if (half === 0) return [{ kind: 'ball', ...mid, angle: 0, r: shape.r }];
+      // The engine's capsule lies along its own y axis.
+      const angle = Math.atan2(b.y - a.y, b.x - a.x) - Math.PI / 2;
+      return [{ kind: 'capsule', ...mid, angle, half, r: shape.r }];
+    }
+    case 'polygon':
+      return shape.pieces.map((piece) => ({ kind: 'convex', points: piece.map(toBody) }));
+  }
 }
 
-function areaOf(shape: ColliderShape): number {
-  return shape.kind === 'circle' ? Math.PI * shape.r * shape.r : shape.w * shape.h;
+function pieceArea(piece: Piece): number {
+  switch (piece.kind) {
+    case 'ball':
+      return Math.PI * piece.r * piece.r;
+    case 'cuboid':
+      return 4 * piece.hw * piece.hh;
+    case 'capsule':
+      return Math.PI * piece.r * piece.r + 4 * piece.half * piece.r;
+    case 'convex':
+      return Math.abs(signedArea(piece.points));
+  }
+}
+
+/** What a piece was built from, rounded, so a rebuild happens when – and only when – it changed. */
+function pieceKey(piece: Piece): unknown {
+  if (piece.kind === 'convex') return piece.points.map((p) => [round(p.x), round(p.y)]);
+  const { kind, ...values } = piece;
+  return [kind, ...Object.values(values).map(round)];
 }
 
 /** A tilemap's cells always block; a collider unless it is a trigger. */